1. Field of the Invention
The present invention relates to a non-contact type flaw detection tracking device for a pipe or tube, by which a flaw detecting sensor disposed opposite to an outer surface of a pipe or tube, for detecting a flaw on a pipe or tube such as a steel pipe or tube, accurately tracks a pipe or tube rotated in a circumferential direction during flaw detection, and an automatic flaw detecting apparatus for a pipe or tube capable of automatically detecting a flaw over the entire length of a pipe or tube including an end of the pipe or tube by using the same. Hereinafter, “pipe or tube” is referred to as “pipe” when deemed appropriate.
2. Description of the Related Art
As a nondestructive inspection method for a pipe, have been known various kinds of flaw detecting methods exemplified by an ultrasonic testing method, an eddy current testing method and a magnetic flux leakage testing method. These flaw detecting methods are generally implemented by relatively rotating a flaw detecting sensor such as an ultrasonic probe in a circumferential direction of a pipe, and further, by relatively moving the flaw detecting sensor in an axial direction of the pipe. In these flaw detecting methods, it is important to maintain positional relationship constant between the pipe relatively rotated in the circumferential direction during flaw detection and the flaw detecting sensor, that is, the positional relationship within a plane perpendicular to the axial direction of the pipe in order to keep a constant flaw detecting sensitivity.
However, it is difficult to maintain relative positional relationship between the pipe and the flaw detecting sensor constant due to the cross-sectional shape of the pipe, vibrations during transportation of the pipe or an influence by a bent pipe at, in particular, an end in the case where the position of the flaw detecting sensor, that is, the position within the plane perpendicular to the axial direction of the pipe is fixed.
In view of this, the flaw detecting sensor is attached to a contact type tracking device for bringing a mechanical contact member such as a roller or a shoe into contact with the pipe principally except for the end of the pipe in the conventional flaw detecting methods, so that a flaw is automatically detected while allowing the flaw detecting sensor to track a positional change of the pipe. In the meantime, ultrasonic testing is performed by manually scanning an ultrasonic probe or magnetic particle testing is performed at the end of the pipe, at which the contact type tracking device is hardly used for the fear of breakage of the contact member.
However, the contact member is liable to be separated from the pipe in the contact type tracking device as the rotational speed of the pipe becomes higher, and therefore, the rotational speed of the pipe must be limited due to degradation of the tracking accuracy of the flaw detecting sensor, thereby raising a problem of deterioration of a flaw detecting efficiency. In addition, the contact member need be brought into contact with the pipe, thereby raising a problem of cumbersome maintenance or a possibility of breakage of the contact member. Moreover, the manual ultrasonic testing or the magnetic particle testing at the end of the pipe requires cumbersome work and degrades the flaw detecting efficiency, and further, the magnetic particle testing, in particular, raises a problem of difficulty in quantifying the detected flaws.
In view of this, there has been desired development of a tracking device of a non-contact type, that is, without the above-described contact member, but being capable of allowing a flaw detecting sensor to track over the entire length of a pipe.
Up to now, non-contact type tracking devices have been proposed in, for example, Japanese Laid-Open Patent Publication Nos. 64-38648, 05-265559 and 2001-208730.
However, a device disclosed in Japanese Laid-Open Patent Publication No. 64-38648 is configured such that a flaw detecting sensor, that is, a probe which tracks a pipe is integrated with a non-contact type displacement gauge, that is, a displacement sensor for measuring the positional relationship between the flaw detecting sensor and the pipe, so as to control the position of the flaw detecting sensor immediately on the basis of the positional relationship between the flaw detecting sensor and the pipe measured by the displacement gauge. Therefore, there arises a problem that high tracking accuracy cannot be achieved because of an operational delay inevitably occurring in positioning means, that is, a servo mechanism disposed in the flaw detecting sensor. In other words, the high tracking accuracy requires a remarkably low rotational speed of the pipe during flaw detection, thereby raising a problem of degradation of flaw detecting efficiency.
In the meantime, a device disclosed in Japanese Laid-Open Patent Publication No. 05-265559 or 2001-208730 is configured such that a flaw detecting sensor tracks, that is, is positioned on a pipe in a stationary state, that is, during non-rotation in a circumferential direction. Therefore, it is difficult to apply such a device to the case of an ever-changing relative position between the flaw detecting sensor and the pipe due to the rotation of the pipe in the circumferential direction.